Halimeda bioherms, formed by calcareous green algae thriving in tropical environments, play a key role in stratigraphy and paleoecology, comparable to coral bioconstructions. Thanks to their rapid calcification process, Halimeda significantly contributes to the production of sediments rich in CaCO₃. These bioherms are concentrated in areas such as the Indonesian K-Bank, the Caribbean, and the Great Barrier Reef of Australia, colonizing seafloors ranging from 2 to 150 meters deep and thriving between 20 and 65 meters, with thicknesses reaching up to 140 meters. In the Mediterranean, Halimeda bioherms are documented exclusively in the pre-evaporitic Messinian, raising questions about the factors limiting their distribution. This study addresses the existing gap by offering a literature review from the Oligocene to the modern era, supported by sedimentological and taphonomic data collected from three Mediterranean areas: the Salento Peninsula, the Sorbas and Nìjar Basins in Spain, and the Heraklion Basin in Crete. The main goal is to analyze depositional environments and compare the bioherms from these unique areas with analogous ones from other regions and different intervals. Field surveys have shown that the bioherms developed in different depositional contexts, forming both isolated mounds and banks along ramp and slope systems. However, the facies are very similar, with textures of rudstone and floatstone, in association with encrusting organisms. The development of Halimeda bioherms in the three studied sites was influenced to varying degrees by environmental, hydrodynamic, and tectonic factors. Local conditions, resulting from the interaction of these factors, led to significant differences in the characteristics of the bioherms, affecting their density, spatial distribution, and size. In the Salento Peninsula, the proliferation of bioherms was favored by nutrient-rich currents driven by upwelling phenomena, while in Spain, bioherms developed more abundantly primarily due to runoff from mountain ranges. Moreover, the influx of nutrient-rich waters from the Atlantic into the Mediterranean likely promoted greater proliferation of bioherms in these areas. As for Crete, the tectonic basin structure of Heraklion positively influenced the influx of terrigenous sediments from surrounding mountain chains, creating ideal conditions for algae growth. Additionally, recent fieldwork conducted here have significantly enriched the documentation on these bioconstructions, highlighting their prevalence in the form of beds rather than mound morphologies. The concentration of Halimeda bioherms in the Mediterranean during the Lower Messinian seems closely related to the configuration of the basin itself, which favored the creation of ideal conditions for their growth. However, the onset of the Messinian Salinity Crisis (MSC) led to their gradual decline. The apparent absence of bioherms in other regions during this interval may be attributed to a lack of documentation. These findings underscore the importance of continuing research on Halimeda bioherms, considering their significance in carbonate production, both in modern and ancient environments. Gaining a deep understanding of these systems is essential not only for reconstructing past marine environments but also for unveiling the dynamics that shaped biodiversity, providing fundamental interpretative keys for understanding paleoenvironmental changes and their future implications.
Le bioerme ad Halimeda, costituite da alghe verdi calcaree che proliferano in ambienti tropicali, rivestono un ruolo fondamentale in stratigrafia e paleoecologia, paragonabile a quello delle biocostruzioni coralline. Grazie al rapido processo di calcificazione, Halimeda contribuisce significativamente alla produzione di sedimenti ricchi di CaCO3. Queste bioerme si concentrano in aree come l'Indonesian K-Bank, i Caraibi e la Grande Barriera Corallina Australiana, colonizzando fondali che variano dai 2 ai 150 metri di profondità e proliferando tra i 20 e i 65 metri, con spessori che possono raggiungere i 140 metri. Nel Mediterraneo, le bioerme ad Halimeda documentate esclusivamente nel Messiniano pre-evaporitico, ha suscitato suscitando interrogativi sui fattori che ne limitavano la distribuzione. Questo studio colma la lacuna esistente offrendo una revisione della letteratura che va dall'Oligocene all'epoca moderna, supportata da dati sedimentologici e tafonomici raccolti in tre aree del Mediterraneo: la Penisola Salentina, i Bacini di Sorbas e Nìjar in Spagna, e il Bacino di Heraklion a Creta. L'obiettivo principale è analizzare gli ambienti deposizionali e confrontare le bioerme di queste aree, uniche in letteratura, con analoghi provenienti da altre regioni e da intervalli differenti. Dai rilievi effettuati è emerso che le bioerme si sono sviluppate in contesti deposizionali differenti, formando sia mound isolati che banchi lungo sistemi di rampa e di scarpata. Tuttavia, le facies risultano molto simili, con tessiture di rudstone e floatstone, in associazione con organismi incrostanti. Lo sviluppo delle bioerme ad Halimeda nei tre siti in esame è stato influenzato da fattori ambientali, idrodinamici e tettonici. Le condizioni locali, derivanti dall'interazione di questi fattori, hanno determinato differenze significative nelle caratteristiche delle bioerme, influenzando la loro densità, distribuzione spaziale e dimensioni. Mentre nella Penisola Salentina, la proliferazione delle bioerme è stata favorita dalla presenza di correnti ricche di nutrienti, alimentate da fenomeni di upwelling, in Spagna le bioerme si sono sviluppate in modo più abbondante principalmente a causa del runoff delle acque meteoriche provenienti dalle catene montuose. Inoltre, l'afflusso di acque ricche di nutrienti dall'Atlantico, convogliate nel Mediterraneo, ha probabilmente favorito una maggiore proliferazione delle bioerme in queste aree. Per quanto riguarda Creta, la conformazione del bacino tettonico di Heraklion ha favorevolmente influito sull’afflusso di sedimenti terrigeni al suo interno provenienti dalle catene montuose circostanti, creando così condizioni ideali per la proliferazione delle alghe. Inoltre, le recenti campagne di ricerca ivi effettuate hanno arricchito significativamente la documentazione riguardante queste biocostruzioni, evidenziando una loro occorrenza prevalente sotto forma di banchi rispetto alle morfologie a mound. La concentrazione di bioerme ad Halimeda nel Mediterraneo durante il Messiniano inferiore sembra essere strettamente legata alla configurazione del bacino stesso, che ha favorito la creazione di condizioni ideali per la loro crescita, mentre l'inizio della Crisi di Salinità Messiniana (MSC) ha determinato il loro progressivo declino. L’apparente assenza di bioerme in altre regioni durante questo intervallo potrebbe essere attribuita alla scarsità di documentazione. Questi risultati evidenziano l'importanza di perseguire la ricerca sulle bioerme ad Halimeda, considerando la loro rilevanza nella produzione di carbonati, sia negli ambienti moderni che fossili. Acquisire una comprensione approfondita di questi sistemi è essenziale non solo per ricostruire gli ambienti marini del passato, ma anche per svelare le dinamiche che hanno plasmato la biodiversità, fornendo chiavi interpretative fondamentali per comprendere i cambiamenti paleoambientali e le loro implicazioni future.
Halimeda bioherms from the pre-evaporitic Messinian successions of the Mediterranean area: a paleoenvironmental archive
PASSASEO, CHIARA
2025
Abstract
Halimeda bioherms, formed by calcareous green algae thriving in tropical environments, play a key role in stratigraphy and paleoecology, comparable to coral bioconstructions. Thanks to their rapid calcification process, Halimeda significantly contributes to the production of sediments rich in CaCO₃. These bioherms are concentrated in areas such as the Indonesian K-Bank, the Caribbean, and the Great Barrier Reef of Australia, colonizing seafloors ranging from 2 to 150 meters deep and thriving between 20 and 65 meters, with thicknesses reaching up to 140 meters. In the Mediterranean, Halimeda bioherms are documented exclusively in the pre-evaporitic Messinian, raising questions about the factors limiting their distribution. This study addresses the existing gap by offering a literature review from the Oligocene to the modern era, supported by sedimentological and taphonomic data collected from three Mediterranean areas: the Salento Peninsula, the Sorbas and Nìjar Basins in Spain, and the Heraklion Basin in Crete. The main goal is to analyze depositional environments and compare the bioherms from these unique areas with analogous ones from other regions and different intervals. Field surveys have shown that the bioherms developed in different depositional contexts, forming both isolated mounds and banks along ramp and slope systems. However, the facies are very similar, with textures of rudstone and floatstone, in association with encrusting organisms. The development of Halimeda bioherms in the three studied sites was influenced to varying degrees by environmental, hydrodynamic, and tectonic factors. Local conditions, resulting from the interaction of these factors, led to significant differences in the characteristics of the bioherms, affecting their density, spatial distribution, and size. In the Salento Peninsula, the proliferation of bioherms was favored by nutrient-rich currents driven by upwelling phenomena, while in Spain, bioherms developed more abundantly primarily due to runoff from mountain ranges. Moreover, the influx of nutrient-rich waters from the Atlantic into the Mediterranean likely promoted greater proliferation of bioherms in these areas. As for Crete, the tectonic basin structure of Heraklion positively influenced the influx of terrigenous sediments from surrounding mountain chains, creating ideal conditions for algae growth. Additionally, recent fieldwork conducted here have significantly enriched the documentation on these bioconstructions, highlighting their prevalence in the form of beds rather than mound morphologies. The concentration of Halimeda bioherms in the Mediterranean during the Lower Messinian seems closely related to the configuration of the basin itself, which favored the creation of ideal conditions for their growth. However, the onset of the Messinian Salinity Crisis (MSC) led to their gradual decline. The apparent absence of bioherms in other regions during this interval may be attributed to a lack of documentation. These findings underscore the importance of continuing research on Halimeda bioherms, considering their significance in carbonate production, both in modern and ancient environments. Gaining a deep understanding of these systems is essential not only for reconstructing past marine environments but also for unveiling the dynamics that shaped biodiversity, providing fundamental interpretative keys for understanding paleoenvironmental changes and their future implications.File | Dimensione | Formato | |
---|---|---|---|
Tesi di dottorato.pdf
embargo fino al 10/04/2026
Dimensione
40.22 MB
Formato
Adobe PDF
|
40.22 MB | Adobe PDF |
I documenti in UNITESI sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/20.500.14242/218698
URN:NBN:IT:UNIFE-218698